Different methods for introducing tritium into organic compounds are known, among which isotope exchange, hydration (including selective) and hydrodehalogenation are preferable. Wherein, the exchange reaction with the participation of gaseous tritium is most preferable for the preparation of tritium-traced saturated and aromatic compounds. A review of the methods for introducing tritium is presented, in particular, in the publication by V. P. Shevhcenko, I. Yu. Nagaev, N. F. Myasoedov “Liphophilic compounds labeled with tritium (Chapter 3).” Moscow, Nauka, 2003.
A solid-phase isotope exchange is the most preferable method of introducing a tritium label into saxitoxin, since it does not require the synthesis of special precursors. However, in order to introduce tritium into this compound, conditions should be selected under which saxitoxin is not destroyed. Furthermore, it is known from prior art that in tritium hydrogenation reactions on palladium heterogenic catalysts, the curves “yield of a radioactive product vs temperature” with a fixed residence time and “yield of a radioactive product vs residence time” upon a fixed temperature pass through maximum (H. W. Cook, W. E. M. Lands, Can. J. Biochem., vol. 53, 1975, p. 1220). Therefore, an important object is also optimization of the conditions of the process for achievement of a product yield that is close to maximum. Taking the aforesaid circumstances into account and carrying out a systematic study, the authors of the instant invention have developed a method for introducing tritium into a saxitoxin molecule in order to prepare a stably-traced product and synthesized tritium-traced saxitoxin satisfying the aforesaid requirements.